Originally Posted by cynjon
The urethane o-rings are a little more durable and probably why they were used in certain areas, but the buna o-rings work just fine and are WAY cheaper, so even if you change them out more frequently, you'll still be money ahead. I've been running all buna in my '06 Evil Minion (PL PM6) and I've had no issues whatsoever. I have urethane o-rings in my rebuild kit, but have never felt the need to use them.
Even in your HPR and LPR? For the bolt system I could see this being fine, but the 2 tiny o-rings in the regs I would not put buna in there.